REDUCING THE RELIANCE ON SYNTHETIC MULTI-SITE FUNGICIDES BY INTEGRATING A BIOPESTICIDE WITH A SINGLE SDHI FUNGICIDE
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Venturia inaequalis (Cooke) G Wint is an ascomycete fungus and the causal agent of apple scab, and economically devastating disease of fresh market apples. The disease is characterized by olive-colored, scabby lesions that develop on leaves and fruit, which leads to reduced yield of marketable fruit (Jones and Aldwinkle, 1990; MacHardy, 1996). A lack of resistance among commercially preferred cultivars has mandates the need for more than 10 fungicide applications per season to manage the disease. Due to a history of sequential resistance development shortly after the introduction of single-site fungicides, apple scab management relies heavily on multi-site fungicides such as mancozeb and captan, which protect trees from a wide range of pathogens from bud break through summer (Agnello et al. 2019; Cox, 2015). Currently, multi-site fungicides are used in rotation with single-site SDHI fungicides to manage apple scab. However, there are concerns about the potential off-target impacts of multi-site fungicides, as well as the environmental impact of excessive application. Due to the negative impacts of commonly used multi-site fungicides such as mancozeb and captan on the environment and human health, some countries have considered restrictions and limitations on the use of mancozeb and captan, making it necessary to reduce the use of multi-site fungicide in management programs. In this study we eavaluate a potential apple scab management program that rotates the biopesticide Serenade Opti (a.i. Bacillus subtilis) with the single-site fungicide Aprovia (a.i. benzovindiflupyr) and compare the disease control to a conventional management program that rotates the multi-site fungicides Manzate Max and Captec (a.i. mancozeb, captan) with the single-site fungicide Aprovia. The programs were tested on two different application schedules (calendar and a schedule determined by the decision support system NEWA), as well as in two different orchard planting styles (vertical axis and modern super spindle) to compare the impact on disease control. Over the course of the study, we found that biopesticides are a potentially viable substitute for multi-site fungicides as a rotational partner for single-site fungicides when paired with decision support systems and modern super spindle plantings. There were no significant differences between management programs using biopesticides and programs using multi-site fungicides in either high or low disease pressure scenarios. Our study supports observations made by Boland (1997), that indicates biological controls are most effective when used in environments less conducive to pathogen development. Overall, this study is a proof-of- concept that demonstrates the feasibility of a management program using biopesticides as a rotational partner with single-site SDHI fungicides, and that the program is comparable to industry standard programs that use multi-site fungicides.
Master of Professional Studies